The present invention relates to an image recording apparatus for recording an image on a photosensitive sheet.
One known image recording apparatus for recording an image on a photosensitive sheet is disclosed in Japanese Laid-Open Patent Publication No. 61-77866, for example. In this conventional image recording apparatus, the photosensitive sheet is exposed to light which has been reflected from an original to be imaged or copied.
Exposure of the photosensitive sheet to such light bearing image information requires a large amount of light energy to be applied to the photosensitive sheet. Therefore, a large-size light source is necessary for applying light to the original, and so is a large-size power supply to energize the light source. For recording or copying color images, it is necessary to employ a special photosensitive sheet which has been processed for dye sensitization as by being coated with sensitized dyes so as to be sensitive to lights in different colors such as red, green, and blue.
The photosensitive sheet disclosed in Japanese Laid-Open Patent Publication No. 61-77866 is shown in FIG. 9 of the accompanying drawings. The photosensitive sheet, designated by the reference numeral 230, comprises a support 220 of paper or film, an aluminum layer 210 deposited on the support 220 by vacuum evaporation, and a photoconductive layer 200 of TiO.sub.2. Since the photosensitive sheet 230 is substantially impermeable to light, it is not suitable for use on an overhead projector. To prepare a sheet for use on an overhead projector, it is necessary to transfer the toner image on the photosensitive sheet 230 onto another transparent film.
There is known an image recording apparatus or copying apparatus including an exposure device employing an intermediate film for forming an intermediate image thereon. Conventional exposure devices of this type have an expensive unit for forming an intermediate image on an intermediate film, and require various highly costly articles to be consumed. To eliminate these drawbacks, there have been devised wire-dot-matrix exposure devices.
To one conventional wire-dot-matrix exposure device, the image of an original is illuminated by an original exposure lamp and focused through a three-color separation filter onto a CCD (charge-coupled device) by a focusing lens. The intensity of light falling on the CCD is converted to an electric signal thereby which is then amplified by an amplifier. The amplified signal is applied to a driver (not shown) which issues a control signal to control a wire-dot-matrix printer head to form a color-separated image on a sheet of plain paper unreeled from a sheet roll with a monochromatic ink ribbon. Therefore, a photosensitive sheet is exposed to light through the paper sheet, serving as an intermediate sheet, and the image thus formed on the photosensitive sheet is developed into a visible image by set-type image developing devices through a known process disclosed in Japanese Laid-Open Patent Publication No. 61-77866. Then, the photosensitive sheet is passed between a pair of image fixing rollers to reproduce a colored image on the photosensitive sheet.
Since inexpensive plain paper may be used as the intermediate sheet, the cost of the exposure device is low.
However, the aforesaid wire-dot-matrix exposure device has proven unsatisfactory in that it is time-consuming to form an intermediate image on the intermediate sheet. Moreover, inasmuch as it is necessary to form three successive intermediate images of different colors on respective three intermediate sheets, these successive intermediate sheets have to be brought into exact registry with each other in order to reproduce a clear colored image.
Generally known color image recording or copying apparatus can be categorized into silver-salt photographic copying apparatus, thermal-transfer copying apparatus, and electrophotographic copying apparatus. The silver-salt color photographic copying system is advantageous in that produced images are of good quality, but disadvantageous in that the time required for a colored image to be produced is long and the system is highly expensive. The thermal-transfer color copying system is problematic because color reproducibility is poor since three color images are superposed on a sheet. The electrophotographic color copying system can copy colored images at the fastest rate and with better resolution.
FIG. 10 of the accompanying drawings shows one general electrophotographic color copying system. A visible-light color separation filter a is angularly positioned such that its red filter element capable of passing red light only is located in a light path, and light emitted from a light source c is applied to a colored original b to scan the original b. Light reflected from the original b is guided by reflecting mirrors d and a lens e to pass through the color separation filter a for forming a red-light latent image on a photosensitive drum f. As the photosensitive drum f rotates about its own axis, the red-light latent image is developed into a visible image with cyan toner by an image developing unit g. After the developed image has been transferred to a recording sheet around a transfer drum h, a green filter element of the color separation filter a is set in the light path, and light is applied to the colored orignal b to form a latent image on the photosensitive drum f. The latent image is then developed into a visible image with magenta toner by the image developing unit g. The developed image is then transferred to the recording sheet. Finally, light reflected from the original b is passed through a blue filter element to form a latent image on the photosensitive drum f, which is developed with yellow toner, and the visible image is then transferred to the recording sheet. After the color-separated images have been transferred to the recording sheet, they are fixed to the recording sheet by an image fixing device j, whereupon the recording sheet with a colored image reproduced thereon is discharged onto a sheet tray k.
In the conventional electrophotographic color copying apparatus, light reflected from the original is separated into colored lights by the red, green and blue filter elements to form respective electrostatic latent images, to which corresponding dry toners are attached. The toners are thereafter transferred to the recording sheet. With the aforesaid system, since the light reflected from the original is separated into color lights, the light energy applied to the photosensitive drum is generally small. Inasmuch as the photosensitive material which the photosensitive drum is made of is less sensitive to light in longer wavelengths, it has been necessary to increase the light output from the light source or the sensitivity of the photosensitive material in the visible light wavelength range has to be adjusted for a higher level.
Various processes have heretofore been available for producing a video hard copies in full colors. These known processes are as follows:
(1) A CRT is used as a light source for emitting light bearing image information to be reproduced on a recording medium such as silver-salt photographic film which may be an instant color film. On example of this system is a silver-salt photographic CRT printer disclosed in Television Society Journal Vol. 40, No. 11 (1986).
(2) An image recording system disclosed in Japanese Patent Publication No. 61-281764 employs a photosensitive pressure-sensitive sheet coated with colorless leuco dyes which will develop colors of cyan (C), magenta (M), and yellow (Y) when brought into contact with a color developer and also with microcapsules made of ultraviolet-curing resin. After the photosensitive pressure-sensitive sheet has been exposed to light bearing image informaiton which is emitted from a CRT that emits ultraviolet radiations having wavelengths of c, m, n, those microcapsules which are not exposed to the radiations and hence not photoset are ruptured under a sufficient pressure to develop colors for thereby developing a color image.
(3) A PPC color electrophotographic copying system employs an electrophotographic photosensitive body made of selenium (Se) or an organic photosensitive material (OPC). After the photosensitive body has been exposed to light representing image information which is emitted from a CRT, and LED, or a laser beam source, the latent image on the photosensitive body is developed successively with toners of C, M, Y. The developed toner image is then transferred onto a sheet of plain paper.
According to the conventional copying systems (1) and (2), the recording medium has independent different spectral sensitivities with respect to image information in red (R), green (G), and blue (B). Therefore, although the wavelengths of lights emitted from the CRT may not necessarily be in full accord with the wavelengths of three primaries, i.e., R=550 nm, G=550 nm, B=450 nm, it has been necessary to provide a recording medium which is sensitive to mutually independent spectral wavelengths which correspond to image information in R, G, B.
With the color image copying system (1), in particular, if an instant color film used as a recording medium is to be interchangeable with a commercially available color photographic film, the CRT must have those types of phosphors which can produce spectral outputs respectively in the wavelengths of R=550 nm, G=550 nm, B=450 nm. However, it is generally difficult to obtain the phosphors of such spectral wavelengths, and hence the color reproducibility of this system has failed to reach an ideal level.
The film used is usually of a cabinet size or a smaller size. Therefore, for reproducing greater image sizes, special films and exposure and fixing devices have to be manufactured and their costs are expensive.
In the color image reproducing process (2), the pressure for rupturing the microcapsules which are not exposed to light to bring their contents into contact with the color developer for color development needs to be in the range of from 500 to 600 Kg/cm.sup.2. Consequently, the pressure developing device required is large in size and highly costly. In order to set the spectral sensitivities of microcapsules to mutually different wavelength ranges corresponding to respective R, G, B image signals, it is necessary to mix sensitizers in the photo-setting resin or to uniformly disperse and coat the microcapsules corresponding to the respective wavelengths on a support. This results in an increased cost of manufacture of the recording medium.
According to the copying system (3), exposure, development, and transfer cycles for image information in R, G, B are independently repeated. Therefore, the exposure light source used may be of a single wavelength output capability, and the spectral sensitivity of the photosensitive body may be in a narrow wavelength range corresponding to that of the light source. However, images produced by this color copying apparatus are inevitably subjected to disturbance due to toner image transfer to the sheet of plain paper. In order to prevent the toner images in C, M, Y from being put out of registry with each other when transferring them onto the sheet, various measures have to be taken to keep a photosensitive drum and a transfer drum on which the sheet of plain paper is wound in exact synchronism with each other. For this reason, the entire apparatus is large in size and complex in structure. In addition, not all color images of any desired lengths can be recorded because of the limited circumferential length of the transfer drum.